Nov. 7 (Bloomberg) -- After a few months of calm ushered in by a truce between Iraq’s Al Jubur tribe and Islamic State, came the curfew and the disappearances.

The two groups had battled for control of al-Alam town, north of Baghdad, over several weeks in June. Sunni tribal elders then sat down with militant leaders and negotiated a deal that allowed Islamic State to raise its black flag, confiscate weapons and run local affairs.

“Everything was good and life was normal,” said Abdel- Latif Khalaf Saleh, a 38-year-old resident. “Until last week, when Abu Raad was appointed as Islamic State’s new emir in al- Alam.”

Since then, hundreds of men and boys, aged 12 to 70, have been rounded up and taken to unknown locations, said Khalaf Saleh and other witnesses interviewed by phone. In other areas of western Iraq, hundreds have been killed.

While the reprisals against Sunni tribes that resisted Islamic State’s drive to establish a caliphate are meant to eradicate opposition, they could have the opposite effect, said Julien Barnes-Dacey, a senior policy fellow at the European Council on Foreign Relations.

“The executions aren’t random mass killings. It’s a powerful message that this is a consequence for those who challenge us,” Barnes-Dacey said by phone. Yet Sunni communities disenfranchised by the Shiite-dominated government and security forces assisted the Islamic State advance. “If that breaks down, it becomes harder,” he said.

Army Officers

One powerful tribal chief, Sheikh Faris al-Dulaimi, a leader of a clan network that formed the backbone of Saddam Hussein’s army for years, has already escalated the fight with Islamic State.

A thousand heavily armed tribal fighters have been sent to areas near the cities of Hit and Zawiya, west of Baghdad, to protect clans being threatened by the militants, Dulaimi said in a phone interview. They’re being led by former army officers and will be joined by government troops soon, he said.

“Islamic State believes the people of these tribes were born Muslims but abandoned their religion when they helped Shiites fighting against them,” al-Dulaimi said, explaining that when the group first entered Anbar province, it killed more than 30 members of his sub-tribe, Albu Assaf, and demolished their houses.

Al-Qaeda Letter

Extreme brutality was also a characteristic of al-Qaeda in Iraq, a previous incarnation of Islamic State. One of its most notorious leaders, Abu Musab al-Zarqawi, took over large areas of the country after the 2003 U.S.-led invasion before he was killed in a U.S. airstrike three years later.

Zarqawi sought to drag Iraqis into a sectarian war, in which he would position himself as the defender of minority Sunnis. That tactic eventually backfired as tribes turned against him during the so-called surge of American troops, something al-Qaeda leaders had warned him about.

A letter written by senior al-Qaeda figure Atiyah Abd al- Rahman, also known as Atiyatullah al-Libi, to Zarqawi in late 2005 refers to Algeria’s civil war, when jihadists lost support after killing hundreds of thousands of their countrymen. “I lived through that myself,” al-Libi said, according to a copy of the letter on the website of the Combating Terrorism Center at West Point. The jihadists “destroyed themselves with their own hands, with their lack of reason.”

‘Increasingly Challenged’

Islamic State leader Abu Bakr al-Baghdadi has been similarly warned over his brutality and harsh treatment of Sunnis by al-Qaeda chief Ayman al-Zawahiri.

“Islamic State will be increasingly challenged from outside and from within,” said Barnes-Dacey. “There was an alliance of convenience formed out of the perceived need to push back against Baghdad, but it’s unlikely to hold.”

Even if the tribes swing behind Iraq’s army, it’s “going to be an enormous challenge to dislodge Islamic State,” he said.

The battle between the Al Jubur and Islamic State in Salahuddin province raged for two weeks. Under the cease-fire deal, the militant group agreed to leave residents alone. “Islamic State betrayed us, they broke the deal and the truce,” said Khalaf Saleh, who has now fled to the city of Kirkuk.

It was the killing of at least 320 members of the Albu Nimr tribe this month, one of the worst massacres committed by the militant group in Anbar province, that convinced him and a group of friends it wasn’t safe to stay.

‘Tide Turning’

“We escaped running through farms, and carrying nothing with us,” he said. “I was starving and thirsty and walked for two days, avoiding main roads.” Separated from his friends, Khalef Saleh said he hitchhiked to the first Peshmerga checkpoint at Kirkuk, where he was met by his brother.

Al-Dulaimi, the tribal leader, said he believes the death toll among Albu Nimr may be double the government estimate of 320. “At first they were killing people with knives, but later, to save time and effort, they began shooting them,” he said. At least 50 bodies were recovered from a well.

Abu Raad is targeting Al Jubur for fighting against Islamic State before the truce and providing a refuge for thousands of people who fled amid a militant offensive in nearby Tikrit, said Bassam al-Juburi, another al-Alam resident who escaped.

“They arrested my cousin so I fled to Kirkuk. I knew what was going to happen,” he said.

In advancing through Syria and Iraq, Islamic State has beheaded, crucified and shot opponents from all ethnic and religious communities, and forced women and girls into marriage.

“This is a group that grew out of the ashes of al-Qaeda in Iraq, which burnt itself out because of the untrammeled level of its brutality and its alienation of Sunnis,” Shashank Joshi, senior research fellow at the Royal United Services Institute in London, said by phone. “ISIL has learnt some of those lessons but is applying them unevenly,” he said, using another name for Islamic State.

“The tide against ISIL may be turning as most Sunnis in Iraq are repelled by what they see even if they aren’t ready to do anything about it.”

To contact the reporters on this story: Zaid Sabah in Washington at zalhamid@bloomberg.net; Caroline Alexander in London at calexander1@bloomberg.net To contact the editors responsible for this story: Alaa Shahine at asalha@bloomberg.net Mark Williams, Karl Maier